a. Field of the Invention
The present invention relates to a lubricating oil pump and, more particularly, to a plunger-type lubricating oil pump for which delivery can be arbitrarily set by operation from outside.
B. Description of the Prior Art
At present, the following type of plunger pump is proposed and put to practical use as a lubricating oil pump. That is, said plunger pump comprises a first plunger, which rotates and slides in axial direction at the same time and has a hole provided from one end thereof toward the inside thereof, and a second plunger slidably fitted into said hole, said plunger pump performing suction and delivery of liquid such as oil by means of periodical change of the volume of the pump chamber caused by relative movement of the first and second plungers. In the above-mentioned type of lubricating oil pump, however, the first plunger performs rotary motion and sliding motion together with the second plunger and, consequently, sliding motion occurs between the inner surface of the cylinder chamber formed in the pump body and outer surface of the first plunger and between the inner surface of the first plunger and outer surface of the second plunger. Therefore, to prevent wear of these surfaces, it is necessary to pay special attention in selection of material and machining of the pump body and first and second plungers and, consequently, the cost of production becomes high. Moreover, as said plunger pump is so constructed that the first and second plungers perform relative movement by respectively performing both of rotary motion and sliding motion, the effective opening area of the passage for communicating the pump chamber to the suction port or delivery port becomes relatively small and, consequently, the pump as a whole becomes large in size compared with its delivery. Besides, when viscosity of the liquid increases as in the case of low temperature, friction is further increased and the pumping efficiency decreases considerably.